1. Field of the Invention
The invention relates to voltage generation and, more particularly, to voltage generation internal to memory systems.
2. Description of the Related Art
Memory cards are commonly used to store digital data for use with various products (e.g., electronics products). Examples of memory cards are flash cards that use Flash type or EEPROM type memory cells to store the data. Flash cards have a relatively small form factor and have been used to store digital data for products such as cameras, hand-held computers, set-top boxes, hand-held or other small audio players/recorders (e.g., MP3 devices), and medical monitors. A major supplier of flash cards is SanDisk Corporation of Sunnyvale, Calif.
FIG. 1 is a schematic diagram of a first conventional voltage generation circuit 100. The conventional voltage generation circuit 100 can provide one or more generated voltages to a memory system that provides non-volatile data storage and represents, for example, a memory card (e.g., flash card). The voltage generation circuit 100 includes a charge pump circuit 102. The charge pump circuit 102 operates to boost a lower input voltage (Vin) to produce a higher output voltage (Vout). The output voltage is coupled to a decoupling capacitor (CD) 104. The output voltage is also coupled to a resistive divider 106. The resistive divider 106 divides the output voltage using resistors R1 and R2. A comparator 108 couples to the resistive divider 106 and to a reference voltage (Vref). The output of the comparator 108 is fed back to the charge pump circuit 102 so that the charge pump circuit 102 can regulate the output voltage so that it remains at a substantially constant voltage level.
FIG. 2 is a schematic diagram of a second conventional voltage generation circuit 200. The conventional voltage generation circuit 200 is generally similar to the conventional voltage generation circuit 100 except that instead of using a resistive divider 106, a capacitive divider 202 is used. The output voltage of the charge pump circuit 102 is coupled to the capacitive divider 202. The capacitive divider 202 divides the output voltage using capacitors C1 and C2. The comparator 108 couples to the capacitive divider 202 and to the reference voltage (Vref). The output of the comparator 108 is fed back to the charge pump circuit 102 so that the charge pump circuit 102 can regulate the output voltage so that it remains at a substantially constant voltage level.
Unfortunately, however, a resistive divider consumes substantial amounts of power. The power consumption is particularly problematic when being used with power conscious electronic devices, such as battery-powered electronic devices. Although a capacitive divider is power efficient, it is not adequately stable given its sensitivity to process variations, parasitic wiring and resistor-capacitor variations and junction leakage currents.
Accordingly, there is a need for improved voltage generation circuits that are not only stable but also power efficient.